Integrated circuits (ICs) and other electronic devices often include field effect transistors (FETs), also called metal-oxide-semiconductor field effect transistors (MOSFETs), or simply MOS transistors or devices. A typical MOS transistor includes a gate electrode as a control electrode and spaced apart source and drain electrodes. A control voltage applied to the gate electrode controls the flow of current through a controllable conductive channel between the source and drain electrodes.
Power and high voltage transistor devices are designed to be tolerant of the high currents and voltages that are present in applications such as physical interfaces, motion control, air bag deployment, and automotive fuel injector drivers. One type of power MOS transistor is a laterally diffused metal-oxide-semiconductor (LDMOS) transistor. In an LDMOS device, a drift space is provided between the channel region and the drain region.
LDMOS devices may be designed to operate in a high-side configuration in which all of the device terminals are level shifted with respect to the substrate potential. Devices configured for high-side operation have been applied in power switchers in DC-to-DC converters, which have respective LDMOS devices for the high side and low side.
LDMOS devices are often used in applications, such as automotive applications, involving operational voltages greater than 45 Volts. Breakdown resulting from applying such high voltages to the drain is often prevented through a reduced surface field (RESURF) structure of the LDMOS device design. The RESURF structure is designed to deplete the drift space in the LDMOS device in both vertical and lateral directions, thereby reducing the electric field near the surface at the drift region and thus raising the off-state breakdown voltage (BVDSS) of the device.
The development of an LDMOS device capable of operating at higher operating voltages typically includes a considerable amount of reliability testing. For example, each new device design is subjected to testing for hot carrier injection (HCI) effects and other gate oxide (GOX) reliability. Significant time and resources are often expended during both the development of devices capable of passing these tests and the implementation of such testing.